Booster pump pulsating when toilet cisterns are nearly full

[Dangerousdave2]

Hi all,
I recently fitted a pump to boost the shower pressure in the house. The plumbing is all flexible pipe and all cold feeds are fed off the same 22mm ring. Taps, toilets, showers and bath, both upstairs and down. Don't know if this is normal, but it is normal in Donegal, North West Ireland!
All works fine except that when the toilet cisterns are near full the pump pulsates on and off till they are full. I am assuming this is caused by the pressure switch being activated / deactivated as the flow drops to a dribble in the cistern. However, after researching on this site, it may be 'hammering' and the pump has flow switches???

The pump is made by / called Techflow. I am planning on replacing it with a larger pump as two new en-suites are being installed. Will a non return valve or a negative head pump sort this?

The pump is located below the hot water cylinder with its own dedicated and thermostatic feeds.

 

[shaky]

Get your plumber back to fit check valves.

 

[BLOD]

Hi dangerousdave2,
might be worth trying a different type of fill valve in the Wc's.

 

[chris watkins]

It is because your existing pumped system is not fitted with an accumulator (similar to potable expansion vessel) which acts as a store of pressure / water & stops the pump from "hunting"

 

[Dangerousdave2]

Thank you for the suggestions. I am not sure if the check valves will work as water still flows into the cistern as the pump is hunting. It is as if the pressure in the pipe builds up and turns the pump off, it then reduces as the cistern fills by a dribble, turning the pump on again which builds the pressure in the pipes up faster than it can be released, turning the pump off.
I just don't know if this logic is correct.
Does an accumulator have a filled pressure and a fill pressure? Ie will it release some pressure before activating the pump?
i am putting a more powerful pump on anyway, so does a negative head pump have an accumulator built in?
thank you again for your time.

 

[chris watkins]

Thank you for the suggestions. I am not sure if the check valves will work as water still flows into the cistern as the pump is hunting.NO IT WON'T WORK
It is as if the pressure in the pipe builds up and turns the pump off, it then reduces as the cistern fills by a dribble, turning the pump on again which builds the pressure in the pipes up faster than it can be released, turning the pump off. SPOT ON
I just don't know if this logic is correct.
Does an accumulator have a filled pressure and a fill pressure? Ie will it release some pressure before activating the pump? YES, IT HAS TO BE SET UP TO SUIT PUMP/SYSTEM BUT IT DOES STORE WATER UNDER PRESSURE & FEEDS IT INTO SYSTEM SO PUMP DOES NOT HAVE TO START.
i am putting a more powerful pump on anyway, so does a negative head pump have an accumulator built in? YES IT WILL HAVE A SMALL ONE TYPICALLY WHICH WILL DO THE JOB
thank you again for your time.

Recommend you get in someone you understands boosted water systems if you intend having one pump supplying a number of bathrooms as there can be lots of issues.

 

[stevetheplumber]

you need presure switches that have a differential setting like these
KPI, Pressure switches for light industry - Danfoss
on and of points are spread apart to stop rapid switching

 

[Dangerousdave2]

Ok. This is starting to make sense! Bear in mind that the house was built in the height of the Celtic Tiger, when anyone who had played with Lego was a property developer and if you could assemble a garden hose you were a plumber. No disrespect to the many proper plumbers out there, but I have just changed the heating system so the hot water is independent of the central heating. My point being that the plumping may not be installed in a sensible way and there are few/no people hearabouts who have experience in this field.

That said, I installed the booster pump!

less sensitive switches may be the answer. It is. However, not a big problem. What I am trying to do is eliminate it when I upgrade the pump.
The water level in the CWST is approx 2-3 feet above the shower, hence the pump.
If I add two more en-suites it will struggle to cope at 1.2 bar (I think)
if I replace it with a 3 bar negative head pump I hope to sort both problems, but am now afraid to ask what the potential other problems are with multiple bathrooms off one pump!!!

 

[stevetheplumber]

just had a thought some ballvalves are fast acting in that the float is in a tank and they fill fast till the last bit and then shut of quick these might be enough to cure the problem

 

[Dangerousdave2]

Thank you to all for your time and input. Fast acting ball valves sound like a good fall back if an accumulator tank / negative head pump doesn't work.

 

[PlumbBobBob]

i would swap the toilet fill valves first before stumping up for a new pump/accumulator £30 against ££££

 

[Chalked]

i would swap the toilet fill valves first before stumping up for a new pump/accumulator £30 against ££££

£30 wasted.
It will still need an accumulator as all ball valves stop quickly or slow the rate down to a trickle. Both will have problems with the whole house boosted by this type of pump.
i would replace the pump with a proper booster set, best get a local plumber round to advise you and look at the system you have to see what is compatible .

 

[Dangerousdave2]

Ok. The pump is being replaced as it won't handle three bathrooms. As for a local plumber with this experience, see above!
i am assuming a 3 bar booster will cope or am I missing something?

 

[chris watkins]

It is not so much the pressure that is important Dave but the flow rate or more precisely the combination of the two.
It is no good having 3bar plus but a dribble of water going to each bathroom likewise having 50l/m @ only 0.5 bar is not going to run your continental high pressure tap fitting.
either speak to pump manufacturers or someone who knows how to read pump graphs.

 

[Ryan LPS]

Your putting these bigger pump in have you got big enough header tanks in loft to coup with the output demand. Have you not thought bout going pressurised cyclinder with a hot 2nd return cos your going to be pushing a lot of dead water about by the snds of it? Dead water = cold water in pipes. Or you could put in a acv cylinder which has I high recovery with a 2nd return.

 

[Dangerousdave2]

I need to investigate flow rate vrs pressure. And yes, the hot water cylinder may need replaced with a bigger one, at which time I will consider a pressurised system. I don't want to spend on a pump that will then be redundant. More research is required
Thank you again to everyone for their input.

 

[Dangerousdave2]

This may be going off topic but the current view is to put a second hot water tank in (possibly pressurised) to service three bedroom en suites, with the current vented tank for one e suite, one toilet, kitchen and main bathroom. The three bedrooms will only be used part time.
This means two separate systems in the one house. If we go this route then the traditional oil fired boiler may be replaced with a condensing one.
All this for a pulsating pump!

 

[chris watkins]

This may be going off topic but the current view is to put a second hot water tank in (possibly pressurised) to service three bedroom en suites, with the current vented tank for one e suite, one toilet, kitchen and main bathroom. The three bedrooms will only be used part time.
This means two separate systems in the one house. If we go this route then the traditional oil fired boiler may be replaced with a condensing one.
All this for a pulsating pump!

Think of it this way Dave you are single-handedly helping to support a failing industry, one which if Lincolnshire is anything to go by only values a plumbing trades person at £8 per hour!!
Keep up the good work.